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How to Select the Best Sand for Your
Bunkers
by James Francis Moore
WITH THE possible exception of green speed, sand bunkers
are the most controversial and discussed features on golf courses,
regardless of the golfer's ability. Predictably, opinions vary widely
on issues such as design, location, playing quality of the sand,
and even what color is best. Generally, there are four major areas
that must be considered when evaluating bunkers. These are sand
selection, architecture, construction, and maintenance.
Selecting the proper sand for bunkers is arguably the most difficult
of these four areas. The makeup of the sand strongly impacts maintenance
and playing quality. The sand can also influence the architecture
and style of construction of bunkers.
There are seven factors that should be considered when selecting
the sand.
- Particle size
- Particle shape and penetrometer value
- Crusting potential
- Chemical reaction (pH) and hardness
- Infiltration rate
- Color
- Overall playing quality
Values for and interpretation of particle size, shape and penetrometer
value, crusting potential, chemical reaction and hardness, and infiltration
rate all should be determined by an accredited physical soil testing
laboratory. Color and overall playing quality are highly subjective
values that are based on personal preference.
As a general guideline, a sand used in bunkers should be composed
of particles with a large majority in the range of 0.25-1.00mm.
Silt and clay (particles below 0.05mm) should be kept to a minimum,
since they are associated with surface crusting. Note that this
size range should be utilized only as a first step in determining
whether the sand is likely to be acceptable overall. In other words,
it is unlikely that a sand that falls significantly outside this
range will perform well in terms of crusting, hardness, porosity,
and/or playing quality. On the other hand, it would be a mistake
to assume that a sand will be appropriate for bunker use simply
because it falls within this particle size range. For example, depending
on particle shape, some sands that fall in this range would be considered
too firm or too soft for play. Since particle size screening is
a simple, inexpensive test that is performed by most sand suppliers,
it is the best first step in determining if the sand is worthy of
further testing.
When evaluating the particle size range of the sand for bunker use,
keep in mind that bunker sand often ends up on the green in surprisingly
large quantities. As golfers blast their way free of the hazard,
the sand is thrown onto the adjacent green. Therefore, when selecting
sand for use in greenside bunkers, the makeup of the green's rootzone
must also be considered. The best rule of thumb is to avoid using
a sand in the green-side bunkers that is significantly finer in
gradation than that used in the rootzone of the green. This is the
same basic rule used for selecting greens topdressing materials.
You can safely lay a coarser material over a finer rootzone mix
without creating significant drainage problems, but just a few topdressings
with a finer material over a more coarsely graded rootzone can cause
drainage problems.
If a bunker sand is selected that is significantly finer in gradation
than the rootzone mixture used in the greens, additional aerification
should be practiced on the affected areas of the green. Backfilling
the aerifier holes with a more coarsely graded sand helps mover
water more rapidly into the rootzone.
Material that is too coarse also can create problems. Particles
greater than 2.00mm are classified as gravel. If present in large
quantities, particles in this range damage mowing equipment and
cause the ball to deflect off line.
The shape of the sand particles has a strong influence on playing
quality and maintenance. A sand particle's shape is classified by
examining both the relative sharpness of the particle's edges and
the overall shape of the particle itself. The surface of particles
can range from very angular (many sharp, well-defined edges) to
well rounded (smooth surfaces). The shape of the particle can range
from low sphericity (an elongated particle) to high sphericity (a
particle that is nearly round).
| Penetrometer
Reading |
Fried-Egg Potential |
| Greater than
2.4 kg/cm2 |
Very
Low tendency to bury |
| 2.2 to 2.4
kg/cm2 |
Slight
tendency to bury |
| 1.8 to 2.2
kg/cm2 |
Moderate tendency to bury |
| Less than 1.8
kg/cm2 |
High tendency to bury |
The angularity and sphericity of the particles have a strong influence
on the playing quality of the sand. For example, a low-sphericity,
very angular sand generally has high resistance to fried-egg lies.
Such sands also tend to stay in place better on the face of the
bunker. However, this same sand would produce very firm bunkers
that some players may find objectionable. Well-rounded, high-sphericity
sands can produce fried-egg lies and are more likely to move off
the bunker face during maintenance and irrigation rainfall.
Sands usually consist of a mixture of particle shapes and sizes.
This is important to the stability and playing quality of the sand.
Again, as a general rule, sands that are highly uniform in size
range and shape (particularly if rounded with high sphericity) tend
to be less stable than a sand that has a wider range of particle
dimensions.
Determining a sand's angularity and sphericity is helpful in predicting
the ultimate playing quality of a bunker, but is by no means an
exact science. The USGA currently is funding research to attempt
to develop better measurement techniques to aid in the selection
of sands for rootzone mixtures and bunkers.
The angularity of the sand is determined by examining the particles
with a microscope and comparing them to the chart in Figure 1 --
Angularity and Sphericity of Sand Particles. After measuring the
angularity, the laboratory performs the penetrometer test to determine
the sand's tendency to produce fried-egg lies. The penetrometer
measures the sand's resistance to compression. The values are reported
in kg/cm2. The potential for fried-egg lies is based on penetrometer
values as described in Table 1 -- Potential for Fried-Egg Lies (Thomas
Turf Services).
Crusting is the formation of a layer of dried, stiff sand on the
surface of the bunker. Such layers typically are 1/8 to 1/4 inch
in thickness, and they severely decrease the playing quality of
the bunker. Sands that are prone to crusting require more frequent
raking to maintain good playing quality. If the crusting potential
is high, the bunkers will require raking following each irrigation
and rainfall event. This greatly increases the labor required to
keep the bunkers in good condition.
Crusting is directly related to the percentage of silt and clay
in the sand. As silt and clay increase, the severity of crusting
increases as well. To test for crusting potential, the laboratory
wets a thin layer of sand and allows it to dry overnight. They then
attempt to lift the layer on the edges using a spatula. Whether
or not a crust has formed will be recorded on the lab test results
and is usually reported as N (none), L (light), M (moderate), or
S (severe).
Some laboratories also test the sand for its chemical reaction (pH).
This value is much less important overall than the other test results
and, on its own, should not be used to disqualify a sand being considered
for use. The pH value provides insight into the chemical makeup
of the sand. A sand with an extremely high pH (> 8.0) is likely
to be strongly calcareous and therefore subject to physical and
chemical weathering.
Sand particles also can change in shape and size due to mechanical
wear. Sand particles that are very soft can be crushed into smaller
particles during raking. A soft sand may play and drain perfectly
at first, only to degrade in quality as the particles are broken
down. Some laboratories now perform a hardness test to determine
the likelihood of this type of degradation.
Infiltration rate refers to the sand's ability to drain. It is also
referred to by laboratories as saturated hydraulic conductivity.
This measurement is most relevant to rootzone mixes for use in putting
greens, but it is also used by some labs to evaluate bunker sands.
Since straight sand is used in bunkers, the initial infiltration
rate measurement is likely to be very high -- often in excess of
50 inches per hour. As a general guideline, a sand being considered
for use in bunkers should drain at a minimum rate of 20 inches per
hour.
Infiltration rate measurements are more useful when evaluating the
suitability of a sand that has been in the bunker for some time.
In most cases, the sand in the bunker gradually becomes contaminated
with the soil from the base and sides of the bunker. This process
occurs more rapidly in bunkers with steep faces and in areas subject
to heavy, frequent rains. A sand that has become heavily contaminated
with soil and organic debris will drain much more slowly than a
sand that is clean. Simply installing new or additional drainage
pipe would be only partially effective under such circumstances.
Complete removal and replacement of the contaminated sand may be
the only complete solution.
Unfortunately, bunker sands occasionally are selected based primarily
on their color. Although sand color is important, since it strongly
impacts the appearance of the course, it should not be given greater
consideration than particle size, particle shape, or crusting potential.
Laboratories measure the color of sand by comparing it to the Munsell
Color Chart. As a general rule, lighter-colored sands are preferred
since they contrast beautifully with the green grass. Color measurements
are also useful when evaluating the visual compatibility of two
sands. An annual task on many courses is to add an inch or two of
sand to existing bunkers to replace what is lost from explosion-type
shots and water and wind erosion. If the new sand is a markedly
different color from the existing sand, it can take months of raking
for the two sands to blend into a uniform color.
Playing quality is unquestionably the
most subjective parameter when choosing bunker sand. The most
important component in the selection process is allowing an
adequate amount of time to fully evaluate the various factors.
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Without question, playing quality is the most subjective evaluation
of bunker sands. Players vary widely in their assessment of what
constitutes good playing quality. One of the few shared opinions
seems to be a desire for all the bunkers on the course to play in
a consistent manner. For this reason, when adding sand to existing
bunkers it is a good practice to perform the work on all of the
bunkers on the course.
From a testing standpoint, particle size, particle shape, crusting
potential, and infiltration rate all provide insight as to how the
sand will play. However, other factors that have nothing to do with
the makeup of the sand have equal if not greater impact on playing
quality. The other factors include:
- Raking frequency
- Raking method
- Green-side irrigation coverage
- Depth of the sand
- Length of time the sand has been in the bunker
The number of times per week the bunker is raked has impact on playing
quality. On courses that rake daily, the possibility of even minor
crusting is eliminated. The upper few inches of the sand remains
loose. The sand also tends to be drier as a result of increased
evaporation. Machine versus hand-raking also affects playing quality.
Hand raking usually results in sand that is firmer and less prone
to fried-egg lies. Machine raking can be either deep (useful to
prevent weed establishment) or very light, depending on the attachment
used.
The green-side irrigation system almost always overlaps into the
bunkers. Thus, during times of the year when it is necessary to
water the greens frequently, the sand in the bunkers will be wetter.
And, since the irrigation system is designed to apply water as evenly
as possible to the surface of the green rather than the surrounding
areas, it is likely the bunkers adjacent to the green will receive
varying amounts of water.
The depth of the sand usually varies even within the same bunker.
The sand is almost always deeper on the low, flat portion of the
bunker and shallower on the faces and slopes. It would be a mistake
to attempt to maintain a consistent depth throughout the bunker.
Golfers should gauge the depth and firmness of the sand while taking
their stance and adjust their shot accordingly.
Sands often change significantly in their playing quality over the
first few months as they become compacted and contaminated with
soil and organic debris. Newly installed sand may seem soft at first,
but soon will become more firm. The speed at which this firming
occurs depends on the angularity and particle sizing of the sand,
as well as raking practices. Since most bunkers are subject to at
least some erosion during irrigation and heavy rainfall events,
the sand will gradually become contaminated with the underlying
and surrounding soil. As a result, the playing quality of the bunker
gradually changes as the bunker ages. The sand particles can also
change in size and shape due to mechanical weathering, as discussed
earlier.
Determining which sand yields the best playing quality is such a
subjective process that a test bunker is often constructed to allow
golfers to field-test the sands for themselves. Assuming three sands
are being considered (each of which has already been evaluated by
an accredited physical soil testing laboratory), use 2 ´ 6's to
divide the test bunker into three areas. Evaluate the sands for
a period of at least two to three months to allow the sand to compact
and better simulate what will happen on the course. Unfortunately,
while this testing process will demonstrate the playing quality
of each prospective sand, it cannot guarantee a unified opinion
among the golfers. The USGA currently is funding research to better
predict the playing characteristics of sands through laboratory
testing.
Several soil testing laboratories provide bunker sand evaluation
services. Usually, a complete analysis can be obtained for less
than $200. The laboratory will need a gallon of dry sand to perform
all of the tests. Be sure to submit a sample of each sand that is
being considered. Allow at least two to three weeks for the laboratory
to complete the tests.
Clearly, there is more to selecting the right sand for your bunkers
than calling the local sand plant and ordering a few truckloads.
Today's golfers (at least in the United States) are becoming increasingly
more demanding of bunkers that play consistently, drain rapidly,
and provide additional beauty to the course. One of the most important
pieces of advice this article can offer is to remember that time
is a necessary component to achieve these goals. Allow plenty of
time for testing to narrow your choices to sands that are properly
sized, stable, and easier to maintain. Time also is needed for the
construction and use of a test bunker to allow golfers to evaluate
the different sands for playing quality. Finally, time will be required
for the newly installed sand to firm up and take on its final playing
characteristics.
JIM MOORE joined the USGA Green Section in 1985, spending his time
conducting Turf Advisory Service visits in the Mid-Continent Region.
In 1996, he assumed the duties of director of the newly formed Construction
Education Program.
Green Section Record Jan/Feb 1998 Vol. 36, #1
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